1. Field of the Invention
The present invention relates to a drive transmission device in which rotary force of a driving source is transmitted to a driven unit through a belt wound around a driving pulley and a driven pulley, and the like.
2. Description of the Related Art
Various known apparatuses, such as image forming apparatuses, include a drive transmission device in which rotary force of a driving source, such as a motor, is transmitted to a driven unit.
For example, in an image forming apparatus, driving force of a motor as a driving source is transmitted to a driving roller which drives a driven unit (for example, a photosensitive drum or an intermediate transfer belt) through a plurality of gears. However, the configuration of transmitting driving force using gears has had a problem that vibrations may occur in the image forming apparatus due to vibromotive force caused by a rotation transmission error (especially, an engagement transmission error) between a driving gear and a driven gear. There has been a possibility that vibrations which have occurred at the gears are transmitted to supporting members, such as a shaft, a bearing, and a side plate, and generate noise.
There has been a known drive transmission device that includes a driving pulley, a driven pulley, and a belt wound around the pulleys, and transmits rotational driving force of a driving source (motor) to a driven unit by using friction force between the individual pulleys and the belt. However, in the case where the driving force is transmitted using such a device, if the driving force is increased excessively, slippage of the belt occurs. Therefore, the driving force of the driving source cannot be transmitted to the driven unit with high accuracy.
As described in Japanese Patent Laid-Open No. 08-146783, there has been a technique of increasing the friction force between a pulley and a belt by allowing electrostatic attraction between the belt and the pulley, and suppressing slippage of the belt. The image forming apparatus described in Japanese Patent Laid-Open No. 08-146783 applies a bias to a core metal of a driving roller as the pulley to cause electrostatic attraction force to act between the driving roller and the intermediate transfer belt, and thus transmits the driving force of the driving roller to the intermediate transfer belt.
In the technique described in Japanese Patent Laid-Open No. 08-146783, the larger the potential difference between the individual pulleys and the belt, the larger the electrostatic attraction force. Therefore, a high voltage is applied to the pulleys to prevent slippage of the belt.
Furthermore, a load applied to a driven unit is not necessarily constant but may vary. Taking into consideration variations of the load onto the driven unit, it is necessary to set a high set value of an applied voltage for the case of the maximum load condition, in order to reliably prevent the occurrence of slippage between the pulleys and the belt. However, applying a high voltage to the pulley or the belt increases power consumption.
The present invention has been designed to solve the problems of the related art. The present invention appropriately suppresses the slippage between a pulley and a belt by efficiently generating a necessary friction force without performing excessive voltage application.